1. Technical Field
The present disclosure relates generally to a built-in antenna for an electronic device, and more particularly, to a multi-band built-in antenna electronic device.
2. Description of the Related Art
A portable terminal is generally considered any hand-held electronic device that can transmit and/or receive an RF signal. Examples of portable terminals include cell phones, smart phones, tablet PCs, personal digital assistants (PDAs), game devices, e-books, digital cameras and navigation devices. As technology has advanced and more functionality has been added to mainstream models, the goal of providing a slim and aesthetic design has remained an important consideration electronic device. Terminal manufacturers are racing to realize the same or improved functions while making the portable terminal smaller and slimmer than older designs.
Modern portable terminals employ at least one built-in antenna for communication functions such as voice and video calls and wireless Internet surfing. Built-in antennas are on a trend of operating at two or more bands (i.e., multi-band), minimizing an antenna mounting space of the portable terminal, reducing a volume thereof, and expanding a function thereof.
A popular design for the multi-band built-in antenna is a Planar Inverted F Antenna (PIFA). For example, a built-in antenna has been designed to cover main frequency bands of Global Systems for Mobile communication (GSM) 900, Digital Cellular Service (DCS) 1800, Personal Communications Service (PCS) 1900, and Wireless Code Division Multiple Access (WCDMA) Band1, and has been widely used. The built-in antenna has been provided for complete coverage of a set of low bands, e.g., GSM 850 and GSM900 switched therebetween through a switching technology using a separately added ground pad. Such “ground-pad switching technology” involves the use of one or more in-line switches between one or more points on the antenna conductor and ground-connected pads to vary an antenna configuration according to the switching states. Switching is performed to optimize antenna performance at a desired band.
In recent years, besides operating at the aforementioned bands, portable terminals using Long Term Evolution (LTE) technology, i.e., the so-called 4th-Generation (4G) are emerging. In some cases, the LTE terminals operate at a frequency band higher than those of 2-Generation (2G) or 3-Generation (3G) bands. For instance, LTE terminals may operate at LTE Band1 (2500 MHz to 2690 MHz), and LTE Band11 (1428 MHz to 1496 MHz). Accordingly, recently released terminals deploy an antenna operating at the LTE Bands separate from an antenna operating at the 2G (GSM900, DCS1800, and PCS1900) and 3G (WCDMA Band1, 2, 5, 8, etc.) bands.
However, with ground pad switching technology, it is difficult to cover a penta band that includes the relatively high bands of LTE Band7 and LTE Band11. Accordingly, the conventional approach is to isolate and mount a GSM Quad-Band antenna and an LTE-Band antenna, separately.
On the other hand, the ground pad switching technology is suitably used at low bands such as GSM900 and GSM850 switched therebetween. The switching states of the switches are controlled to shift the resonant frequency of the antenna for operation at one band or the other. However, using this scheme, the amount of frequency shift obtainable is limited to about 60 MHz. This limitation stems from the difficulty in securing as much spaced distance between radiators. as desired. Ground pad switching technology can increase a frequency shift but has been known to change antenna impedance and deteriorate basic antenna performance. Also, the capability of covering at least two high bands of 1 GHz or more such as DCS band (1710 MHz to 1850 MHz) and LTE Band11 (1428 MHz to 1496 MHz) is desirable. In this case, the band centers are separated by about 300 MHz. In order to switch between these bands using ground pad switching technology, a complex design is needed, which undesirably trades off antenna performance. Thus, separate antennas are typically provided for the two bands.
Accordingly, the aforementioned application of the separate antenna runs counter to the recent trend of simultaneously realizing slimming down and multi-functionality of the electronic device. Furthermore, the added antenna and complexity increases manufacturing cost.